Principal

A principal is an entity that has been authenticated and can subsequently be assigned permissions through authorization. A principal is most often a human user, but the term is deliberately broader. A service, or a process running on a system, can equally be authenticated and granted its own permissions, and so is just as much a principal as a person is.

The term is used throughout the Java platform’s security model, and appears in various authentication protocols and standards, including GSSAPI and Kerberos, as the generic name for "whoever – or whatever – has been identified."

Using one word for users, services, and processes alike lets an authorization model be defined once, over principals in general, without needing separate rules for each kind of identity it might apply to.